function [x,y,i] = metodParabola(f,x1,x2,err,maxIter)
x3 = x2;
x2 = (x1+x3)/2;
for i = 1 : maxIter;
    A = [1 x1 x1^2; 1 x2 x2^2; 1 x3 x3^2];
    b = [feval(f,x1); feval(f,x2); feval(f,x3)];
    p = A\b; % koeficijenti zeljene parabole
    xopt = -(p(2)/(2*p(3))); % vrednost optimuma
    y2 = feval(f,x2);
    yopt = feval(f,xopt)
    if( yopt >= y2)
        if ( xopt >= x2 )
            x1 = x1;
            x2 = x2;
            x3 = xopt;
        else
            x1 = xopt;
            x2 = x2;
            x3 = x3;
        end
    else
        if ( xopt >= x2 )
            x1 = x2;
            x2 = xopt;
            x3 = x3;
        else
            x1 = x1;
            x3 = x2;
            x2 = xopt;
        end
    end
    if( abs( polyval(p,xopt) - feval(f,xopt)) <= err)
      x = xopt;
      y = feval(f,xopt);
      break;
    end
end